Semiconductor devices often use a common silicon device to provide different or varying levels of functionality. Such differences in functionality are needed to support the use of the silicon device in different target environments. The use of the silicon device in a different target environment includes changing the address of the silicon device as seen on a control bus.
When extra functionality is added to a semiconductor device as the design of semiconductor evolves, it is necessary that the semiconductor device functions identically in a system to a previous part with no changes to the printed circuit board (PCB) layout. Such a change may be achieved by software. However, with other systems there may not be a controlling host device. Due to a lack of a controlling device, configuration pins provide a solution. Common silicon is often configurable by connecting one or more pins to a high or low logic level. In small standard packages, there may not be enough available pins to allow all of the necessary configuration settings, especially for test modes. When a part is an upgrade of a previous product with additional functionality, the pin count must remain the same, but the additional functionality will still need to be switched on or off. Where the added functionality is needed, a board change is acceptable. However, when it is necessary to maintain backward compatibility, the device packaging cannot be changed. Testing purposes provides another case where extra modes are needed. Changes to the board layout for testing purposes are not significant.
Adding more configuration pins to a part where no pins are available or using existing spare pins will allow more device configurations to be selected. However, adding more configuration pins to a part will increase the need to change existing board layouts. As the package changes the parts will become non-interchangeable. Standard packages and the correct number of pins may not be available. In small devices, the cost of the packaging is a significant part of the overall product cost.
It would be desirable to provide a method and/or apparatus that implements multi-bit configuration pins to eliminate the need to change existing board layouts and eliminate non-interchangeable standard packages.